Depending on how careful you are and what equipment you've got on hand, you might be able to detect that going on, but I think "easily" is a stretch.
If there is a secret involved in this it would be undocumented commands sent by the network to phones that then interpret them as commands to connect to the network, plus baseband processors the periodically look for such commands. They don't radiate, so very little power is used, but they should be entirely dormant.
If there is a secret involved in this it would be undocumented commands sent by the network to phones that then interpret them as commands to connect to the network, plus baseband processors the periodically look for such commands. They don't radiate, so very little power is used, but they should be entirely dormant.